Possible influence of desert dust on seedability of clouds in Israel

The first experiment, Israeli-1 (1961-67), had a crossover design. Its overall seeding effect was an enhancement of 15% of the rainfall in the target areas, significant at 0.9%. The second experiment, Israeli-2 (1969-75), had a generally similar crossover statistical design to that of Israeli-1 but with some modifications that allowed a separate evaluation of the north target area alone. The seeding effect obtained for the north alone was 13%, significant at 2.8%. Based on this, clouds in northern Israel have been seeded operationally since 1975, while randomized experimental seeding is continuing in the south as Israeli-3. Reanalyses of the experiments, stratified by observations of dust haze, show an increase of 26% in Israeli-2 north on the 202 "no-dust' days and no effect on the remaining 182 "dust' days. According to Israeli-2 south and Israeli-3, the indicated seeding effects in the south were also more positive by 16% on the "no-dust' days than on the "dust' days. -from Authors